I am a software engineer who has always had the passion of eletronics. Recently I decided to really get into it, get my self an arduino and study electronics really well to have a deep understanding of how to build a circuit and try to understand the physics behind it (to the point where I know what I am building and why).
I am trying to learn so I apologize if I ask a stupid question or I am concentrating on the wrong thing, but my intent is not to just get an answer and build a circuit, but to actually understand each single part of what I am doing.
I have a couple of questions on the simplest circuit you can build, the classic Arduino Hello World.
I attached the circuit everyone recommends building.
The Arduino specs (as you guys probably already know) are the following: output pins: 5V, 40mA
The LED specs are the following: 1.8-2.2 V, 20mA max
So, here are my questions:
Why when I am building a circuit, I need to limit current but not voltage? in other words, the resistor won’t modify the voltage of the output, it will just limit the current on the other side of it. If the LED supports max 2.2V, wouldn’t it get ruined by sending 5V to it?
I first tried to connect the led directly to the arduino and it worked without the LED breaking or anything. Does that mean that even if the specs say max 20mA, the LED actually supports more?
if I do the calculation by hands, I find that a 330 Ohms resistor is too much but maybe I am doing the wrong calculation:
Arduino outputs 40mA, but LED needs max 20mA. I need to find a resistor such that it blocks 40 - 20 = 20ma
R = V / I → R = 5V / 0.02A → R = 250 Ohms
So why can I put a 330 Ohms resistor and it still works?
330 = 5 / I → I = 15mA.
Am I not blocking too little current? Arduino sends 40mA, I am blocking 15 so I am sending 25mA.
Also it’s kind of not intuitive that as I use a bigger resistor I am blocking LESS current, but maybe I am not understanding something.
It seems that as the resistor tends to INFINITE, I am blocking close to 0 current, which doesn’t sound intuitive.
- Is that any resistor that will block so much current that the led won’t turn on?
I was thinking:
R = 5V / 0.04 A → 125 Ohms. Does this mean that if I put a 125 Ohms resistor I will block all current and the LED won’t turn on?
- Electrons go from negative to positive but the model says current is going from positive to negative. Is that why I need to put the resistor BEFORE the + goes into the led? Is it any useful if I put it after?
Thanks in advance for the reply, hopefully I will get a better understanding of this as times goes by.
circuit.tiff (41.1 KB)